Cheating on a Sick Spouse

Edwards' betrayal of his wife at her most vulnerable moment -- as a cancer patient -- is more common than conventional wisdom suggests, according to infidelity experts.

A mistress of former House Speaker Gingrich told Vanity Fair they had their tryst as his first wife recovered from uterine cancer surgery in the 1980s.

While McCain was married to his first wife, who was disabled from a car accident, he was "aggressively courting a 25-year-old woman who was as beautiful as she was rich," according to a New York Times colunmist's account of the 1970s incident that predated McCain's election to the Senate.

Both McCain and Gingrich have admitted to the affairs.

"It's not that uncommon for the spouse of a seriously ill person to commit adultery," said Anthony DeLorenzo, who, with his wife, founded infidelity.com. "The healthy spouse often feels guilty, lonely and helpless about the illness, and that combination can make a spouse more vulnerable to having an affair."

Sickness frequently interferes with or eliminates sex from a relationship, making a healthy spouse more vulnerable to advances or situations that lead to sex outside of marriage, the New Jersey private detective told ABCNews.com.

Blogs this week have been less sympathetic, calling Edwards and his extramarital sex with videographer Rielle Hunter "very low" and "depraved."

"Edwards claimed, while engaging in the affair, that Elizabeth was in remission," read one post on the site, the World According to Matt. "In short he is a cad."

Relationship experts like DeLorenzo, who counsels wronged spouses on his Web site, say about 60 percent of men and 40 percent of women stray during the course of a marriage.

"I know Edwards spoke of his narcissism as a factor, but far more than that had to be going on," said DeLorenzo, who has handled many cases of cheating.

And it's not just the men who are going astray. One middle-aged man who was confined to a hospice-like setting suspected his wife was having an affair when he got no answer to his telephone calls to her on Friday and Saturday nights, DeLorenzo said.

"His wife took care of him three or four times a week, but she was in her 50s and was still a young person," DeLorenzo said. After receiving the report confirming the affair, the man eventually accepted his wife's dalliances.

But according to Thomas Nagy, who is on the clinical faculty at Stanford School of Medicine and works with couples dealing with cancer, that and other chronic diseases can have an especially devastating effect on a marriage.

Depression, anxiety and medications can take a toll on the spouse who is the patient.

"It hugely impacts on moods and emotional intimacy -- everything," Nagy said. "Mental health treatment is extremely important. Most are not in spousal support or marriage counseling."

He advocates for mandatory marital counseling whenever a partner faces a serious illness.

In Cancer, Illness 'Trumps Everything'

"The mental health needs of a marriage aren't paid attention to because the medical illness trumps everything," Nagy said.

The Edwards couple -- at the center of political power -- got the "one-two punch," according to Nagy. "His wife is having cancer in this really high-profile fast life."

But women who have been wronged have less sympathy for the senator and more for his wife.